Definition of endo, exo, syn, anti

Descriptors of the relative orientation of groups attached to non-bridgehead atoms in a bicyclo[x.y.z]alkane (x y > z > 0). if the group is orientated towards the highest numbered bridge (z bridge, e.g. C-7 in example below) it is given the description exo; if it is orientated away from the highest numbered bridge it is given the description endo. if the group is attached to the highest numbered bridge and is orientated towards the lowest numbered bridge (x bridge, e.g. C-2 in example below) it is given the description syn; if the group is orientated away from the lowest numbered bridge it is given the description anti. See also syn, and anti.